Random Shutdowns

I have an original MacBook Pro 15" (A1150) that randomly shuts down. Seems to be running very hot. I've already had to replace a bulging battery, and TechTool Pro has indicated a temperature-related S.M.A.R.T. failure with the HD.

If I downgrade the HD from 7200 RPM to 5400 RPM, will that help with the heat issues? Any other heat-related fixes?

I know the 13" MacBook Pro suffered a random shutdown syndrome, but I didn't know if the 15" was affected too. TIA.

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